This research is directed towards understanding the cardiovascular and metabolic aspects of electrolyte transport in the kidney. Studies are designed to examine the adaptive changes which occur in the kidney to maintain electrolyte balance as renal function declines. Interest is directed especially towards cellular adaption changes which govern the secretion of potassium. In addition, studies are conducted to evaluate the effect of lithium on the renal transport of water and electrolytes in various portions of the nephron using micropuncture techniques. BIBLIOGRAPHIC REFERENCES: Kaufman, J.M., Hardy, R. and Hayslett, J.P. Age dependent characteristics of compensatory renal growth. Kid. Inter. 8:21-26, 1975. Finkelstein, F.O. and Hayslett, J.P. Role of medullary Na-K-ATPase in renal potassium adaptation. Amer. J. Phys. 229:524-528, 1975.